In vitro nonbutanol-extractable iodine release in dog thyroid

Modelling of macrophage responses to biomaterials in vitro: state-of-the-art and the need for the improvement

The increasing use of medical implants in various areas of medicine, particularly in orthopedic surgery, oncology, cardiology and dentistry, displayed the limitations in long-term integration of available biomaterials. The effective functioning and successful integration of implants requires not only technical excellence of materials but also consideration of the dynamics of biomaterial interaction with the immune system throughout the entire duration of implant use. The acute as well as long-term decisions about the efficiency of implant integration are done by local resident tissue macrophages and monocyte-derived macrophages that start to be recruited during tissue damage, when implant is installed, and are continuously recruited during the healing phase. Our review summarized the knowledge about the currently used macrophages-based in vitro cells system that include murine and human cells lines and primary ex vivo differentiated macrophages. We provided the information about most frequently examined biomarkers for acute inflammation, chronic inflammation, foreign body response and fibrosis, indicating the benefits and limitations of the model systems. Particular attention is given to the scavenging function of macrophages that controls dynamic composition of peri-implant microenvironment and ensures timely clearance of microorganisms, cytokines, metabolites, extracellular matrix components, dying cells as well as implant debris. We outline the perspective for the application of 3D systems for modelling implant interaction with the immune system in human tissue-specific microenvironment avoiding animal experimentation.

American Thyroid Association Guide to investigating thyroid hormone economy and action in rodent and cell models

BACKGROUND

An in-depth understanding of the fundamental principles that regulate thyroid hormone homeostasis is critical for the development of new diagnostic and treatment approaches for patients with thyroid disease.

SUMMARY

Important clinical practices in use today for the treatment of patients with hypothyroidism, hyperthyroidism, or thyroid cancer are the result of laboratory discoveries made by scientists investigating the most basic aspects of thyroid structure and molecular biology. In this document, a panel of experts commissioned by the American Thyroid Association makes a series of recommendations related to the study of thyroid hormone economy and action. These recommendations are intended to promote standardization of study design, which should in turn increase the comparability and reproducibility of experimental findings.

CONCLUSIONS

It is expected that adherence to these recommendations by investigators in the field will facilitate progress towards a better understanding of the thyroid gland and thyroid hormone dependent processes.

Role of caveolin-1 in thyroid phenotype, cell homeostasis, and hormone synthesis: in vivo study of caveolin-1 knockout mice

In human thyroid, caveolin-1 is localized at the apex of thyrocytes, but its role there remains unknown. Using immunohistochemistry, (127)I imaging, transmission electron microscopy, immunogold electron microscopy, and quantification of H(2)O(2), we found that in caveolin-1 knockout mice thyroid cell homeostasis was disrupted, with evidence of oxidative stress, cell damage, and apoptosis. An even more striking phenotype was the absence of thyroglobulin and iodine in one-half of the follicular lumina and their presence in the cytosol, suggesting that the iodide organification and binding to thyroglobulin were intracellular rather than at the apical membrane/extracellular colloid interface. The latter abnormality may be secondary to the observed mislocalization of the thyroid hormone synthesis machinery (dual oxidases, thyroperoxidase) in the cytosol. Nevertheless, the overall uptake of radioiodide, its organification, and secretion as thyroid hormones were comparable to those of wild-type mice, suggesting adequate compensation by the normal TSH retrocontrol. Accordingly, the levels of free thyroxine and TSH were normal. Only the levels of free triiodothyronine showed a slight decrease in caveolin-1 knockout mice. However, when TSH levels were increased through low-iodine chow and sodium perchlorate, the induced goiter was more prominent in caveolin-1 knockout mice. We conclude that caveolin-1 plays a role in proper thyroid hormone synthesis as well as in cell number homeostasis. Our study demonstrates for the first time a physiological function of caveolin-1 in the thyroid gland. Because the expression and subcellular localization of caveolin-1 were similar between normal human and murine thyroids, our findings in caveolin-1 knockout mice may have direct relevance to the human counterpart.

Preferential megalin-mediated transcytosis of low-hormonogenic thyroglobulin: a control mechanism for thyroid hormone release

Hormone secretion by thyrocytes occurs by fluid phase uptake and lysosomal degradation of the prohormone thyroglobulin (Tg). However, some Tg internalized by megalin bypasses lysosomes and is transcytosed across cells and released into the bloodstream. Because the hormone content of Tg is variable, we investigated whether this affects transcytosis. We found that rat Tg with a low hormone content [low-hormonogenic rat Tg (low-horm-rTg)] is transcytosed by megalin across thyroid FRTL-5 cells to a greater extent than rat Tg with a high hormone content [hormonogenic rat Tg (horm-rTg)]. In immunoprecipitation experiments, the Tg sequence Arg-2489-Lys-2503 (required for binding to megalin and heparan sulfate proteoglycans) was found to be more exposed in low-horm-rTg, which accounted for its preferential transcytosis. Thus, removal of surface heparan sulfate proteoglycans from FRTL-5 cells or blocking of 2489-2503 reduced transcytosis of low-horm-rTg to a greater extent than that of horm-rTg. Preferential transcytosis of low-horm-rTg affected hormone release. Thus, the increase in hormone release from horm-rTg in FRTL-5 cells determined by megalin blocking (due to reduced transcytosis and enhanced Tg degradation) was rescued by low-horm-rTg, suggesting that megalin is required for effective hormone release. This finding was confirmed in a small number of megalin-deficient mice, which had serological features resembling mild hypothyroidism. Reduced hormone formation within Tg in vivo, due to treatment of rats with aminotriazole or of patients with Graves' disease with methimazole, resulted in increased Tg transcytosis via megalin, in confirmation of results with FRTL-5 cells. Our study points to a major role of megalin in thyroid homeostasis with possible implications in thyroid diseases.

Effect of amiodarone and propranolol on the functional properties of human thyroid follicles cultured in collagen gel

Amiodarone and propranolol have been known to inhibit the peripheral conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) but their direct effect on the thyroid gland is not understood. We therefore investigated the action of the two drugs on the functional properties of human thyroid follicles embedded in collagen gel. Amiodarone and propranolol induced a dose-dependent reduction or blocking of the follicular production of cyclic AMP (cAMP), thyroglobulin (Tg) and free triiodothyronine (FT3) under 200 microU/ml medium. Small drug doses and the drug solvents did not affect the follicular secretion. The inhibiting effect of amiodarone and propranolol on follicular production of cAMP, Tg and FT3 appears to result from several factors: (1) inhibition of thyroid 5'-deiodinase; (2) amiodarone high iodine content; (3) a quinidine-like effect of propranolol involving a membrane-stabilizing mechanism.

Modulation of thyroglobulin release by dog thyroid slices

Nonbutanol-extractable 131I (NBE131I) release by dog thyroid slices in vitro has been shown previously to be primarily thyroglobulin (Tg); it is stimulated by TSH. NBE131I (Tg) release has therefore been considered as an in vitro model of thyroglobulin secretion and was further characterized in this work. TSH-stimulated NBE131I (Tg) release, like TSH-stimulated BE131I (T4, T3 and iodide) release was reproduced by forskolin, an activator of adenylate cyclase. TSH-, (Bu)2cAMP- and forskolin-stimulated NBE131I (Tg) release was inhibited by 10(-5) M carbamylcholine, an effect relieved by 10(-5) M atropine, but not by 10(-4) M 1-methyl-3-isobutylxanthine. NBE131I (Tg) release was observed in the presence of 2 mM methimazole and 2 mM perchlorate. Cooling the slices to 20 degrees C or addition of 10(-5) M monensin completely blocked the formation of apical pseudopods and BE131I release but not NBE131I (Tg) release. Inhibition by 500 microM chloroquine of intralysosomal Tg hydrolysis and BE131I release did not enhance NBE131I (Tg) release. Cytochalasin B induced a concentration-dependent increase in basal and TSH-stimulated NBE131I (Tg) release at concentrations which depressed TSH-stimulated BE131I release. Removal of Ca2+ from the medium and slices by 10(-3) M or 10(-4) M EGTA increased NBE131I (Tg) release. In conclusion, in dog thyroid slices, TSH-stimulated NBE131I (Tg) release was mediated by cAMP and inhibited by 10(-5) M carbamylcholine at a step beyond cAMP. It was not neosynthesized Tg. It did not seem to require the formation of apical pseudopods or to result from the escape from lysosomes of undegraded thyroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of cyclic AMP action in the dog thyroid by its agonist and antagonist Sp- and Rp-adenosine 3',5'-monophosphorothioate

The diastereoisomeric forms of adenosine 3',5'-monophosphorothioate, Sp-cAMPS and Rp-cAMPS, have been shown to mimic and to inhibit activation of protein kinase type I and type II by cyclic AMP. In the present work, Sp-cAMPS mimicked thyrotropin (TSH) action on thyroid hormone secretion and protein iodination in dog thyroid slices, whereas Rp-cAMPS antagonized those effects. The phosphorothioates have been tested as inhibitors or activators of the three major phosphodiesterases: the Ca2+/calmodulin-sensitive form, the cyclic GMP-stimulated form and the cyclic AMP-specific enzyme. At 100 microM Sp-cAMPS inhibited the three enzyme activities. In contrast, Rp-cAMPS failed to stimulate activity of the three enzymes. From a comparison of the biological properties of Sp- and Rp-cAMPS and 3-isobutyl-1-methyl xanthine, it is suggested that one site of action of the phosphorothioates is on the cyclic AMP-dependent protein kinases, i.e. the effects of Sp-cAMPS and Rp-cAMPS observed in intact cell can be ascribed to the agonistic and antagonistic effects on the cyclic AMP-dependent protein kinases. However, partial inhibition of phosphodiesterase activities by the phosphorothioates cannot be excluded.

Further characterization of the iodide inhibitory effect on the cyclic AMP system in dog thyroid slices

Iodide inhibits cyclic AMP accumulation in the thyroid by a process which is prevented by inhibition of iodide uptake and of thyroid peroxidase. By a similar process, it also exerts other independent effects such as the enhancement of iodinated protein release. Iodide inhibited the stimulation of adenylate cyclase by prostaglandin E1, cholera toxin and forskolin. The action of iodide was not relieved by phosphodiesterase inhibitors and was not additive with the effect of norepinephrine or adenosine. Iodide did not decrease the cellular level of ATP. The data are compatible with an inhibition of adenylate cyclase beyond the level of the receptor, presumably at the level of the catalytic unit or its interaction with the positive transducing unit NS. The effect of iodide required TSH for its expression but not for its installation. It was decreased under all conditions in which iodide organification was decreased: decreased iodide or increased methimazole concentration, absence of calcium in the medium, etc. However, the relation between iodide binding to proteins and effect was not linear. The effect was not relieved by washing in the absence of iodide and in the presence of perchlorate, but it was partly reversible in the presence of methimazole propylthiouracyl or thiourea. It was not relieved by cooling to 20 degrees C and cytochalasin b, which block stimulated thyroglobulin hydrolysis and iodothyronine release, nor by actinomycin D, cycloheximide, puromycin, mepacrine or indomethacin. The data suggest that iodide binds to a saturable cell component by a reaction which is reversible only in the presence of thiol-containing drugs.

Specific staining of the thyroid follicular cell apical membrane by nitroblue tetrazolium

Nitroblue tetrazolium (NBT) has been widely used to demonstrate redox systems, particularly in phagocytizing polymorphonuclear leukocytes. Based on the striking similarities between redox metabolism in leukocytes and in the thyroid, we studied NBT reduction by microscopic techniques and NBT effects in thyroid metabolism in dog-thyroid slices in vitro. We observed specific localization of NBT reduction product along the apical membrane of the follicular cell. Hence, NBT is a potentially useful market of thyroid-cell polarity.